As methods and apparatuses for packing a material into the space formed by a rubber mold with a cavity, punch and a cylindrical body into which the punch is inserted, or a container, a bag or a space enclosed with boards or the like, the following have been known:
The method in which a material to be packed is weighed with an automatic weighing device and then the material is packed into a container, and the method in which a measuring cup is used to measure the volume of the material to be packed and then the material is packed into a container.
Another well known packing method is shown in FIG. 26. A container(s) formed with a cylinder (1) and a punch (2) inserted therein is filled with a material provided in a box (3) having an opening in the bottom, by driving a piston rod (4) of a cylinder (not shown) so that the box (8) slides on the table 5 and cylinder (1) to be the box (8) and attached to a driving axis (6a) or a motor (6), container(s) is filled with the material.
The packing methods described above may ensure accurate weighing of material. However, in those methods, not only the weighing process, but also the packing process takes time, therefore they are not good in terms of work efficiency. In addition, due to the generally poor flowability of material such as powder, packing of weighed material into the cavity is not smoothly carried out, which consumes even more time. The poor flowability causes material to form bridges, and pores and voids tend to generate in such a material. Therefore, the density of the material filled into the container becomes uneven, especially in containers with complex shapes. In the powder compaction methods in which a powder is compacted in a cavity of a die or a rubber mold, the unevenness of the density of the material filled into the container (cavity) reduces the near-net-shape performance of the compacts and causes cracking or chipping of the compacts. A good packing method without having such problems has long been sought.
In the method using measuring cups or the like, the disadvantage is that if the material has poor flowability, bridges are formed in the material to be weighed. The bridges cause pores to form in the material, which affects the accuracy of the volume measurement.
Also, in the method illustrated in FIG. 26, due to the poor flowability of the powder, the material does not smoothly pour into the cavity(s) from the box (3). Therefore, it takes time to fill the cavity(s) with the powder, and bridges tend to form in the powder packed in the cavity, causing uneven distribution of the powder in the cavity(s). It is difficult for this method to perform the packing evenly throughout the cavity, and moreover, if the container has a complex shape or long and narrow shape, the unevenness of the packing density in the cavity becomes a serious problem.
In addition to the unevenness of the packing density described above, conventional packing methods and apparatuses for packing material have the disadvantage of low packing density of the material because of bridges and voids formed in the material packed in the cavity. In the die pressing method, if the powder in the cavity has a low packing density, the upper and lower punches have to move a long distance. This causes such problems as the powder is caught between the punches, and the unevenness of the density of the compact in the direction parallel to the pressing direction becomes very large. In the pressing methods using rubber molds such as rubber isostatic pressing method (RIP), and cold isostatic pressing method (CIP), in which a rubber mold is filled with a powder and then pressed in water or oil is used, the problem is that the obtained compacts have a so-called obvious "elephant foot" deformation. In products sold in the form of a container filled with powder, if the packing density is low at the time of the production though it appears to be fully packed with powder, because the density is increased by vibration or other causes during the transportation, a large space is formed in the container which reduces the quality of the product.
It is the object of this invention to solve the problems described above and to provide a method and apparatus for packing a material into a container rapidly as well as uniformly and in a highly densified condition throughout the container. Packing techniques in the fields of powder metallurgy or the packaging industry can be improved by this invention.